Trailers for road vehicles have various electrical lights, such as brake, tail lights and indicator lights. These are powered and controlled from the tow vehicle.
The electrical connection from the trailer to the tow vehicle is usually via a detachable multi strand cable. Typically the tow vehicle has a socket mounted at its rear into which a plug on the cable of the trailer is inserted. To allow for movement of the trailer relative to the tow vehicle the cable cannot be taut and there must be extra cable, i.e. some slack, to accommodate this relative movement.
When the trailer is detached from the tow vehicle the plug is removed from the socket and then hangs from the loose cable. The plug and cable can present a safety hazard when manoeuvring a trailer. For example a person manoeuvring the trailer may trip on the cable. In addition, the plug and cable may be damaged or contaminated with debris, such as dirt. Most single axle trailers are balanced so the trailer hitch rests on the ground when unloaded. The cable and plug are at the hitch end and commonly either rest on the ground, where they can be contaminated or can be crushed by the trailer hitch.
Electrical connectors are typically provided in one or two forms. In one form the connector is in a fully assembled form, with the cable permanently attached to the electrical pins or sockets and, usually encased in a moulded shell. The other form is for attachment to a cable at a later date. Permanently attached cables typically are connected to rolled terminals that are crimped to the electrical wire. Connectors for which the cable is attached later are typically provided with terminals formed of solid metal that has been machined to have a bore for the wire and a threaded side aperture for a screw. Whilst these allow a cable to be attached and detached they are more expensive than rolled terminals.